In the past, the eastern Brazilian marmosets (penicillata É. Geoffroy, 1812, geoffroyi É. Geoffroy in Humboldt, 1812, aurita É. Geoffroy in Humboldt, 1812, and flaviceps Thomas, 1903) of the “jacchus group” were considered to be subspecies of Callithrix jacchus, following Hershkovitz (1977). All are now considered to be full species (see Coimbra-Filho 1984, Mittermeier et al. 1988, Marroig et al. 2004, Coimbra-Filho et al. 2006).

Coimbra-Filho (1986a,b, 1990, 1991) has argued that the similarity in dental morphology (Natori 1986), behaviour, pelage (infants of the two forms are practically identical in appearance), and vocalizations (Mendes 1997b,c) and the recent discovery of wild groups of hybrid C. aurita and C. flaviceps at Carangola, Minas Gerais (Ferrari and Mendes 1991), argue for their subspecific status (Coimbra-Filho et al. 1993). Ferrari et al. (1996) studied and reviewed the ecology and behaviour of C. aurita and C. flaviceps groups and concluded that although undoubtedly very similar, the “comparison appears to have done more to re-emphasize the enormous flexibility underlying the behavioural ecology of the marmosets as a whole than clarify the relationships between these two taxa in particular” (p.167).

Justification:
This species is considered Vulnerable due to small population size and ongoing decline. Current estimates of the population are less than 10,000 mature individuals, with no subpopulation greater than 1,000 individuals. Remaining subpopulations are fragmented. Densities are naturally low.

Callithrix aurita occurs in the montane rain forests of south-eastern Brazil, in the southern part of the state of Minas Gerais, the state of Rio de Janeiro, and the east and north-east of the state of São Paulo (see Coimbra-Filho 1986b; Olmos and Martuscelli 1995; Brandão and Develey 1998; Ferrari et al. 1996). Hershkovitz (1977) marks the northern limit in Minas Gerais as the Rio Muriaé, but it occurs to the north in the Rio Doce State Park in Minas Gerais (Mittermeier et al. 1982), and hybrids (with C. flaviceps) have been recorded at Carangola in the Serra do Brigadeiro, Minas Gerais (Ferrari and Mendes 1991; Mendes 1997a,d; Cosenza and Melo 1998). Hershkovitz (1977) indicated the south-easternmost locality to be the Rio Ribeira de Iguapé in São Paulo. However, Olmos and Martuscelli (1995) failed to find evidence for this. They reported that extensive fieldwork (1982-1995) in such localities as the Fazenda Intervales State Park, Alto Ribeira State Park, Ilha do Cardoso and Carlos Botelho, and the Jureia Ecological Station and the muncipalities of Juquitiba amd Miracatú in the Serra da Paranapicaba consistently failed to find C. aurita. They proposed the southern limit to be near the city of São Paulo, north of the junction of the Rios Pinheiros and Tietê. The Rio Tieté forms the southernmost boundary and the most southerly record is close to Ipanema (23º26’S, 47º36’W), today Araçoiaba da Serra (the type locality for Leontopithecus chrysopygus). From there it extends west between the upper reaches of the Rios Tieté/Piracicaba. Again the exact limits are unclear, but believed by Olmos and Martusecelli (1995) to be the junction of these two rivers.

Brandão and Develey (1998) carried out surveys to understand better the range of C. aurita. Although generally believed to be largely montane in its range (600-1,200 m according to Olmos and Martuscelli (1995) and 500-800 m according to Rylands (1994)) museum specimens have been collected in the foothills of the Serra do Mar, south of Rio de Janeiro: Pedra Blanca, municipality of Paratí at 80 m, and Mambucaba, municipality of Angra dos Reis at 100 m (Brandão and Develey 1998). Coimbra-Filho (1991) and Mendes (1993) also indicated that it occurred elsewhere in lowland Rio de Janeiro, including the north-east, but is probably today extinct there. All recent records are montane. Brandão and Develey (1998) carried out extensive surveys of the lowland coastal forests of São Paulo and Rio de Janeiro and were unable to obtain evidence of the species’ existence anywhere except at Mambucaba where they found one in captivity and observed a group at 165 m.

This marmoset has been recorded north of the Rio Paraíba do Sul at the following sites: Mogi-Guaçú (Rio Mogi-Guaçú) by R. A. Mittermeier (unpubl.) and Muskin (1984); Alfenas, upper Rio Grande, in Minas Gerais (Hershkovitz 1977; Muskin 1984a); Vargem Grande, São Paulo (Muskin 1984a); Fazenda Monte Alegre, Monte Belo, Minas Gerais (Muskin 1984a) and in the vicinity of Viçosa, Minas Gerais (Mendes 1993); Serra do Capanema, Rio de Janeiro (21º03’S, 42º03’W) (Mendes 1993), Fazenda João Abdo, Rio de Janeiro (21º27’S, 41º56’W) (Mendes 1993). The westernmost locality shown by Hershkovitz (1977, p.490) is Boracéia, north-east of Bauru, on the upper Rio Tieté (22°10'S, 48°45'W), but Olmos and Martuscelli (1995) found this to be an outlier and suggested that locality really refers to the Boracéia Biological Station near the headwaters of the Rio Tietê.

Callithrix aurita is nowhere common, and populations in the National Parks of Bocaina and Serra dos Orgãos are minimal (Coimbra-Filho 1984). Nine months of surveys in the Carlos Botelho State Park in the Serra do Paranapiacaba, in the south of its range, failed to provide any evidence for populations of this marmoset (Paccagnella 1991; see also Torres de Assumpção 1983). Although recorded as rare in the Itatiaia National Park by Ávila-Pires and Gouveia (1977), Mittermeier et al. (1982) reported it extinct there, although it may still occur in very reduced numbers (Coimbra-Filho 1986b). It is extremely rare in the private reserve of the Fazenda Barreiro Rico (3,259 ha of forest), São Paulo. Milton and Lucca (1984) estimated no more than 8–12 animals in the entire area.

Callithrix aurita occurs in the montane rain forests and forests of the inland plateau, at altitudes up to 1,300 m, where dry season temperatures can fall close to freezing (Ferrari et al. 1996; Brandão and Develey 1998). Callithrix aurita and C. flaviceps are the southernmost forms of marmosets in terms of the natural range of the genus (C. jacchus, C. penicillata and C. geoffroyi have been introduced further south in Paraná, São Paulo, Santa Catarina and Argentina). There is what would appear to be a natural hybrid zone with Callithrix flaviceps, at the Serra do Brigadeiro, Carangola, in south-eastern Minas Gerais (Coimbra-Filho et al. 1993; Cosenza 1993; Cosenza and Melo 1998).

Marmosets and tamarins are distinguished from the other monkeys of the New World by their small size, modified claws rather than nails on all digits except the big toe, the presence of two as opposed to three molar teeth in either side of each jaw, and by the occurrence of twin births. They eat fruits, flowers, nectar, plant exudates (gums, saps, latex) and animal prey (including frogs, snails, lizards, spiders and insects). Marmosets have morphological and behavioural adaptations for gouging tree trunks and branches and vines of certain species to stimulate the flow of gum, which they eat, and in some species form a notable component of the diet (Coimbra-Filho 1972; Rylands 1984). They live in extended family groups of between four and 15 individuals. Generally, only one female per group breeds during a particular breeding season. Brandão (1999) recorded a home range of 39.9 ha (extending as high as 1,350 m above sea level) for one group at the Bananal Ecological Station, São Paulo.

The ecology and behaviour of C. aurita has been studied by Muskin (1984a,b) and Martins (1998a,b; Martins and Setz 2000; Santos and Martins 2000) in southern Minas Gerais, Brandão (1999; Brandão and Devely 1998) at the Bananal State Ecological Station, and by Corrêa (1995; Ferrari et al. 1996; Corrêa et al. 2000) and Coutinho (1996; Coutinho and Corrêa 1995) at the Núcleo Cunha of the Serra do Mar State Park in São Paulo, Brazil. Coutinho (1996) studied particularly the social and reproductive behaviour.

The dentition of Callithrix aurita is less specialized for tree-gouging to obtain gum than it is in C. jacchus and C. penicillata (see Natori 1986). Despite this, gum is an important part of the diet year round, and largely obtained from sites where it is available without requiring gouging (Muskin 1984a,b; Coimbra-Filho 1991; Corrêa 1995; Ferrari et al. 1996; Martins and Setz 2000). Martins (2000) recorded them foraging for prey over army ant (Eciton burchelli) swarms. Notable for this species is its consumption of fungi, otherwise recorded only in Callimico goeldii. They find the fruiting bodies of these fungi on the stems of bamboos Merostachys sp. and the South American mountain bamboo Chusquea sp., both of the family Poaceae.

The widespread destruction of the forests within its range, especially, for example, along the valley of the Rio Paraiba, and in the lowlands is a major threat to this species (Coimbra-Filho 1986b; Brandão and Develey 1998). It might still remain in some areas of the lowland forests of Rio de Janeiro (e.g., Mambucaba, Angra dos Reis), but is believed extinct from lowland forest in the state of São Paulo (Brandão and Develey 1998).

These animals are sometimes hunted for pets. It is possible that introduced Callithrix jacchus and Callithrix penicillata have competed, and still are competing, with and displacing this species in Rio de Janeiro and Sao Paulo particularly. Many non-native Callithrix are also interbreeding with C. aurita resulting in hybridization, although the extent of this threat needs further investigation.